1. Technical Field
The present invention is directed toward antennas, and more particularly toward antennas for use with signals in different frequency bands.
2. Background Art
Antennas are an important component of those devices which communicate by radio waves. The ability to reliably send and receive signals is largely dependent on proper functioning of the antenna.
The performance of any antenna, specifically quantified by its radiation pattern and feedpoint impedance characteristics, is fundamentally controlled by the electric current distribution established upon the radiating structure by the associated input (excitation source). For portable and mobile radio communications applications, the optimum radiation pattern characteristics are defined by a single omni-directional pattern lobe with the principal axis of the lobe situated at 90 degrees with respect to the radiating structure.
For applications involving multi-band portable and mobile radio terminals, and more specifically for applications involving three or more bands of operation, optimum radiation characteristics are difficult to obtain for all bands when using simple radiating structures. In general, if a simple radiating structure, such as a monopole, is designed for low-band operation in a multi-band application, the resulting harmonically related current distributions resulting from excitation at the higher frequency bands will not yield the required radiation pattern characteristics for the higher bands. If the simple radiating structure is, by contrast, designed for high-band operation in a multi-band application, the feedpoint impedance bandwidth is restrictively narrow at the lower frequency bands, thus complicating and increasing the cost of the associated antenna-radio impedance matching circuitry. Given the growing competition in the field of radio communications, cost of all components, including antennas, is an important consideration.
The present invention is directed toward overcoming one or more of the problems set forth above.